Shexiang Tongxin dropping pill protects against isoproterenol-induced myocardial ischemia in vivo and in vitro

Shexiang Tongxin dropping pill (STDP) is a formulae of Chinese Medicine commonly used to treating angina pectoris in China. However, its mechanism of action is still yet unclear. This study investigated the roles of STDP on myocardial ischemia injury. We constructed a rat model of myocardial injury (isoproterenol subcutaneous injection, i.h, 85 mg/kg/day for 2 days), and compared among 4 groups: CON (control), ISO (ischemic injury model), MET (metoprolol), and STDP. Serum contents of Troponin I (cTnI), creatine kinase (CK), CK-MB, lactate dehydrogenase (LDH), alpha-hydroxybutyric dehydrogenase (α-HBD), and Aspartate Aminotransferase were detected and five STDP doses (1, 10, 100, 1000 and 10000 mg/kg/day) were chosen to obtain a dose-response curve. Western-blot was used to detect phosphorylations of extracellular signal-regulated kinase 1/2 (ERK1/2), protein kinase B (AKT), and camodulin kinase II (CamkII). Furthermore, an ERK1/2 inhibitor PD98059, a phosphatidylinositol-3-kinase inhibitor, LY294002, and a CamKII inhibitor, KN-93 were administered i.h. RESULTS cTnI, CK, CK-MB, α-HBD, and LDH were significantly lower in STDP than ISO (P<0.05). STDP exhibited a dose-dependent effect with a half maximal inhibitory concentration of 42 mg/kg/day. Phosphorylation of ERK1/2 was enhanced in the STDP group (vs. ISO, P<0.05), while AKT and CamkII were not changed. Further, the protective effects of STDP were offset by PD98059 administration i.h. In conclusion, STDP protected against the ISO-induced myocardial ischemic injury via an ERK1/2 signaling pathway, which provided a mechanism to support clinical applications of STDP as treatment for ischemic heart disease.